Embodiments of the present invention relate to a multi-phase electric circuit comprising an electric machine, as well as comprising an inverter, wherein the machine encompasses a rotor, which is connected to the inverter via at least two brushes per phase.
Such an electric circuit is known, for example, from DE 10 2008 009 276 A1 or from DE 10 2008 064 079 A1. The stator of the asynchronous machine is connected therein to an electric energy supply grid and the rotor is connected to the energy supply grid via an inverter. The inverter can be constructed, for example, of two inverters, which are realized by means of power semiconductor devices, and a DC link, which is connected there between and which encompasses at least one capacitor.
The rotor can be set into rotation, for example with the help of wind power or water power or the like. If the rotor then carries out a rotation, electric energy is fed into the energy supply grid by means of the voltage, which is induced into the stator.
Due to its rotation, the rotor must be electrically connected to the inverter via brushes. In the case of asynchronous machines with higher performance, it can thereby be necessary to provide for a plurality of brushes for each phase. This can have the result that an undesired asymmetrical current flow is created via the brushes due to production-related differences between the brushes, which belong to a phase, for example.
A short-circuiting device, a so-called crowbar, is often connected to the connecting line between the rotor and the inverter. If a malfunction is determined during the operation of the electric circuit, the short-circuiting device is activated. This has the result that the three phases, which are supplied to the short-circuiting device, are short-circuited.